This invention relates to a liquid jetting head for ejecting a liquid droplet from a nozzle orifice by causing pressure fluctuation to occur in liquid in a pressure chamber as a piezoelectric vibrator becomes deformed.
Liquid jetting heads each for ejecting a liquid droplet from a nozzle orifice by causing pressure fluctuation to occur in liquid in a pressure chamber include a recording head, a liquid crystal jetting head, a color material jetting head, and the like, for example. The recording head is installed in an image recording apparatus such as a printer or a plotter for ejecting ink liquid as ink droplets. The liquid crystal jetting head is used with a display manufacturing apparatus for manufacturing liquid crystal displays. In the display manufacturing apparatus, a liquid crystal ejected from the liquid crystal jetting head is poured into a predetermined grid of a display substrate having a large number of grids. The color material jetting head is used with a filter manufacturing apparatus for manufacturing a color filter, and ejects a color material onto the surface of a filter substrate.
Various types of liquid jetting heads are available, one of which is a liquid jetting head for ejecting liquid droplets by deflecting and deforming piezoelectric vibrators formed on the surface of a vibration plate. This liquid jetting head is made up of an actuator unit including pressure chambers and piezoelectric vibrators and a flow passage unit including nozzle orifices and a common liquid reservoir, for example. In the liquid jetting head, a piezoelectric vibrator on the vibration plate is deformed, whereby the volume of the corresponding pressure chamber is changed for causing pressure fluctuation to occur in liquid stored in the pressure chamber. Using the pressure fluctuation, a liquid droplet is ejected from the corresponding nozzle orifice. For example, the pressure chamber is contracted, whereby liquid is pressurized for pushing out the liquid from the nozzle orifice.
In such a liquid jetting head, a drive signal is supplied to each piezoelectric vibrator 53 of an actuator unit 52 through a discrete terminal 51, for example, as shown in FIG. 11. The drive signal is supplied using a film-like wiring board 54 such as an FPC (flexible printed circuit) or a TCP (tape carrier package), as shown in FIG. 12. The wiring board 54 is formed with a conductor pattern on the surface of a base film of polyimide, etc., and the conductor pattern except contact terminals 55 is covered with a resist 59 (see FIG. 14). Since the discrete terminals 51 are formed in a state in which they are arranged like rows, the contact terminals 55 are also formed in a state in which they are arranged like rows. Since the liquid jetting head has a plurality of the actuator units 52 placed side by side, the wiring board 54 must be overlaid on the actuator unit 52.
Each piezoelectric vibrator in deflection vibration mode has a piezoelectric body layer sandwiched between a common electrode and a discrete electrode; for example, the discrete electrode is extended toward one side of the vibrator in the longitudinal direction thereof for electric connection to the discrete terminal 51, and branch common electrode is extended toward an opposite side of the vibrator in the longitudinal direction thereof for electric connection to a proximal common electrode 56. Since the proximal common electrode 56 is positioned on an opposite side to the connection terminal 51 with the piezoelectric body layer between, each piezoelectric vibrator at the vibrator row end is used as a dummy vibrator and the proximal common electrode 56 and the discrete terminal 51 are electrically connected via a connection electrode 57 deposited on the surface of the dummy vibrator. Each branch common electrode is adjusted to a common potential through the discrete terminal 51. For example, a GND line is electrically connected to the discrete terminal 51, thereby adjusting each branch common electrode to a ground potential.
The connection electrode 57 is formed using two or three (in FIG. 11, two) piezoelectric vibrators (dummy vibrators) 53 from the row end, for example. Since the number of the piezoelectric vibrators (drive vibrators) 53 involved in ejecting liquid droplets is large (for example, several tens), the connection electrode needs to be made thick so as to allow much electric current to flow without a hitch. Therefore, to form the connection electrode, printing is used and a coat of a paste-like electrode material about 10 to 20 μm thick is applied via a mask.
In the connection electrode 57 thus formed on the surfaces of the dummy electrodes, a burr-like part pointed upward easily occurs in an edge portion; this is a problem. The possible reason is that when the mask is lifted up and removed after a coat of the electrode material is applied, the edge portion of the electrode material is also lifted up as the mask is removed.
The connection electrodes 57 and conductor patterns 58 on the wiring board cross as shown in FIGS. 12 and 13. Thus, as the burr-like part of the connection electrode 57 is baked and hardens, it is anxiety that the burr-like part would stick into the resist 59 when the wiring board 54 is attached, for example, as shown in FIG. 14. In this case, the extension direction of the connection electrode 57 crosses that of the conductor pattern 58 and thus if the burr-like part deeply sticks into the resist 59, it is anxiety that the conductor pattern 58 will be short-circuited or broken.